Both the retinoblastoma gene (RB) and transcription factor E2F play a critical role in cell growth control (for a review, see Adams, P. & Kaelin, W. Seminars in Cancer Biology 6:99-108 (1995)). The RB locus is frequently inactivated in a variety of human tumor cells. Reintroduction of a wild-type RB gene (e.g., Bookstein et al. Science 247:712-715 (1990)) or RB protein (pRB) (e.g., Antelman et al. Oncogene 10:697-704(1995)) into RBneg/RBmut cells can suppress growth in culture and tumorigenicity in vivo.
While E2F serves to activate transcription of S-phase genes, its activity is kept in check by RB. RB arrests cells by blocking exit from G into S-phase (for example, Dowdy et al. Cell 73:499-511 (1993)) but the precise pathway of the arrest remains unclear.
Although E2F forms complexes with RB, complex formation is more efficient if an E2F-related protein, DP-1, is present. E2F-1 and DP-1 form stable heterodimers which bind to DNA (for example, Qin et al. Genes and Dev. 6-:953-964 (1992)). DP-l-E2F complexes serve to cooperatively activate transcription of E2F-dependent genes. Such transcription can be repressed by pRB in the same manner as E2F-1 or DP-1 activated transcription.
Transcriptional repression of genes by RB in some instances can be achieved by tethering pRB to a promoter. For example, GAL4-pRB fusions bind to GAL4 DNA binding domains and repress transcription from p53, Sp-1 or AP-1 elements (Adnane, et al. J. Biol. Chem. 270:8837-8843 (1995); Weintraub, et al. Nature 358:259-261 (1995)). Sellers, et al. (Proc. Natl. Acad. Sci. 92:11544-11548 (1995)) disclosed fusions of amino acid residues 1-368 of E2F with amino acids 379-792 or 379-928 of RB.
Chang, et al. (Science 267:518-522 (1995)) disclosed the use of a replication-defective adenovirus-RB construct in the reduction of neointima formation in two animal models of restenosis, a hyperproliferative disorders.